The idea that sickness has an odour was explored in an experiment by a team led by Mats Olsson at the Karolinska Institute in Stockholm.

"He dressed eight healthy volunteers in tight, cotton T-shirts and injected one half of the group with a placebo and the other half with a chemical that gave them a mild flu-like reaction.

"A month later, the participants came back and were injected with the other solution - the one they had not received the first time. All the T-shirts were then collected and patches from the underarm area were cut out and placed in squeeze bottles. These were used to supply puffs of air to a panel of smelling volunteers."

For Olsson, one of the most interesting findings was that people seemed capable of sniffing out disease early on.

Here, according to Alphus D Wilson and Manuela Baietto's Advances in Electronic-Nose Technologies Developed for Biomedical Applications, published in Sensors, is what diseases smell like: